Pacemaker retrieval systems and methods

ABSTRACT

A catheter system for retrieving a leadless cardiac pacemaker from a patient is provided. The cardiac pacemaker can include a docking or retrieval feature configured to be grasped by the catheter system. In some embodiments, the retrieval catheter can include a snare configured to engage the retrieval feature of the pacemaker. The retrieval catheter can include a torque shaft selectively connectable to a docking cap and be configured to apply rotational torque to a pacemaker to be retrieved. Methods of delivering the leadless cardiac pacemaker with the delivery system are also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation application of co-pending U.S. patent application Ser. No. 16/214,709, filed Dec. 10, 2018, which is a Continuation application of U.S. patent application Ser. No. 14/816,302, filed Aug. 3, 2015, now issued as U.S. Pat. No. 10,188,425, entitled “Pacemaker Retrieval Systems and Methods,” which is a Continuation application of U.S. patent application Ser. No. 13/324,802, filed Dec. 13, 2011, now issued as U.S. Pat. No. 9,126,032, entitled “Pacemaker Retrieval Systems and Methods,” which claims the benefit of U.S. Provisional Patent Application No. 61/422,622, filed Dec. 13, 2010, titled “Pacemaker Retrieval Systems and Methods”, each of which is incorporated herein by reference in its entirety.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

FIELD

The present disclosure relates to leadless cardiac pacemakers, and more particularly, to features and methods by which they are removed from the heart. More specifically, the present disclosure relates to features and methods for retrieving a leadless cardiac pacemaker from tissue.

BACKGROUND

Cardiac pacing by an artificial pacemaker provides an electrical stimulation of the heart when its own natural pacemaker and/or conduction system fails to provide synchronized atrial and ventricular contractions at rates and intervals sufficient for a patient's health. Such antibradycardial pacing provides relief from symptoms and even life support for hundreds of thousands of patients. Cardiac pacing may also provide electrical overdrive stimulation to suppress or convert tachyarrhythmias, again supplying relief from symptoms and preventing or terminating arrhythmias that could lead to sudden cardiac death.

Cardiac pacing by currently available or conventional pacemakers is usually performed by a pulse generator implanted subcutaneously or sub-muscularly in or near a patient's pectoral region. Pulse generator parameters are usually interrogated and modified by a programming device outside the body, via a loosely-coupled transformer with one inductance within the body and another outside, or via electromagnetic radiation with one antenna within the body and another outside. The generator usually connects to the proximal end of one or more implanted leads, the distal end of which contains one or more electrodes for positioning adjacent to the inside or outside wall of a cardiac chamber. The leads have an insulated electrical conductor or conductors for connecting the pulse generator to electrodes in the heart. Such electrode leads typically have lengths of 50 to 70 centimeters.

Although more than one hundred thousand conventional cardiac pacing systems are implanted annually, various well-known difficulties exist, of which a few will be cited. For example, a pulse generator, when located subcutaneously, presents a bulge in the skin that patients can find unsightly, unpleasant, or irritating, and which patients can subconsciously or obsessively manipulate or “twiddle”. Even without persistent manipulation, subcutaneous pulse generators can exhibit erosion, extrusion, infection, and disconnection, insulation damage, or conductor breakage at the wire leads. Although sub-muscular or abdominal placement can address some concerns, such placement involves a more difficult surgical procedure for implantation and adjustment, which can prolong patient recovery.

A conventional pulse generator, whether pectoral or abdominal, has an interface for connection to and disconnection from the electrode leads that carry signals to and from the heart. Usually at least one male connector molding has at least one terminal pin at the proximal end of the electrode lead. The male connector mates with a corresponding female connector molding and terminal block within the connector molding at the pulse generator. Usually a setscrew is threaded in at least one terminal block per electrode lead to secure the connection electrically and mechanically. One or more O-rings usually are also supplied to help maintain electrical isolation between the connector moldings. A setscrew cap or slotted cover is typically included to provide electrical insulation of the setscrew. This briefly described complex connection between connectors and leads provides multiple opportunities for malfunction.

Other problematic aspects of conventional pacemakers relate to the separately implanted pulse generator and the pacing leads. By way of another example, the pacing leads, in particular, can become a site of infection and morbidity. Many of the issues associated with conventional pacemakers are resolved by the development of a self-contained and self-sustainable pacemaker, or so-called leadless pacemaker, as described in the related applications cited above.

Self-contained or leadless pacemakers or other biostimulators are typically fixed to an intracardial implant site by an actively engaging mechanism such as a screw or helical member that screws into the myocardium.

SUMMARY OF THE DISCLOSURE

A catheter for retrieving a medical device from a patient is provided comprising, a handle, a catheter shaft coupled to the handle, a snare disposed within the catheter shaft and extendable distally beyond the catheter shaft, a docking cap disposed on a distal portion of the catheter shaft, the docking cap being rotatable independent of the catheter shaft, and a torque shaft disposed within the catheter shaft and selectively connectable to the docking cap, the torque shaft configured to rotate within the catheter shaft to apply rotational torque to the docking cap when connected to the docking cap.

In some embodiments, the catheter further comprises an interference feature disposed on an interior surface of the docking cap, the interference feature configured to engage a corresponding interference feature on the medical device to be retrieved. In some embodiments, the interference feature comprises a ridge.

In some embodiments, the catheter further comprises slot disposed inside the docking cap, the slot configured to engage a key on the torque shaft. In one embodiment, the torque shaft is configured to apply rotational torque to the docking cap when the docking cap slot is engaged with the key on the torque shaft.

In another embodiment, a proximal portion of the torque shaft is coupled to a control knob on the handle. In some embodiments, longitudinal movement of the torque knob along the handle causes the torque shaft to engage or disengage the slot in the docking cap. In another embodiment, rotation of the control knob causes the torque shaft and docking cap to rotate when the key on the torque shaft is engaged with the docking cap slot. In yet another embodiment, longitudinal movement of the control knob along the handle moves the torque shaft and snare longitudinally.

In some embodiments of the catheter, the snare comprises a plurality of loops. In other embodiments, the snare comprises a single loop. In one embodiment, the single loop comprises a loop perpendicular to the catheter shaft. In other embodiments, the snare is offset from a longitudinal axis of the catheter when the snare is advanced distally beyond the catheter shaft.

A leadless pacemaker and retrieval system is provided, comprising a leadless cardiac pacemaker having a retrieval feature coupled to the pacemaker with at least one flexible stem, and a delivery catheter comprising a handle, a catheter shaft coupled to the handle, a snare disposed within the catheter shaft and extendable distally beyond the catheter shaft, a docking cap disposed on a distal portion of the catheter shaft, the docking cap being rotatable independent of the catheter shaft and being sized and configured to receive the retrieval feature of the leadless cardiac pacemaker, and a torque shaft disposed within the catheter shaft and selectively connectable to the docking cap, the torque shaft configured to rotate within the catheter shaft to apply rotational torque to the docking cap when connected to the docking cap, and to apply rotational torque to the leadless cardiac pacemaker when the pacemaker is disposed in the docking cap.

In some embodiments, the catheter further comprises an interference feature disposed on an interior surface of the docking cap, the interference feature configured to engage a corresponding interference feature on the pacemaker. In some embodiments, the interference feature comprises a ridge.

In some embodiments, the catheter further comprises slot disposed inside the docking cap, the slot configured to engage a key on the torque shaft. In one embodiment, the torque shaft is configured to apply rotational torque to the docking cap when the docking cap slot is engaged with the key on the torque shaft.

In another embodiment, a proximal portion of the torque shaft is coupled to a control knob on the handle. In some embodiments, longitudinal movement of the torque knob along the handle causes the torque shaft to engage or disengage the slot in the docking cap. In another embodiment, rotation of the control knob causes the torque shaft and docking cap to rotate when the key on the torque shaft is engaged with the docking cap slot. In yet another embodiment, longitudinal movement of the control knob along the handle moves the torque shaft and snare longitudinally.

In some embodiments of the catheter, the snare comprises a plurality of loops. In other embodiments, the snare comprises a single loop. In one embodiment, the single loop comprises a loop perpendicular to the catheter shaft. In other embodiments, the snare is offset from a longitudinal axis of the catheter when the snare is advanced distally beyond the catheter shaft.

A method of retrieving a medical device from a patient is also provided, comprising positioning a snare of a catheter in proximity to a retrieval feature of the medical device, grasping the retrieval feature of the medical device with the snare, pulling the snare proximally into the catheter to position the retrieval feature of the medical device inside a docking cap of the catheter, and applying rotational torque from the docking cap to the medical device to unscrew the medical device from tissue in the patient.

In some embodiments, the medical device comprises a leadless cardiac pacemaker.

In one embodiment, the applying rotational torque step further comprises rotating a torque shaft coupled to the docking cap. In another embodiment, the applying rotational torque step further comprises engaging a key feature on the torque shaft with a matching slot in the docking cap.

In some embodiments, the method further comprises covering the medical device with a protective sheath and removing the device from the patient.

In some embodiments, the grasping step further comprises grasping the retrieval feature with a loop of the snare. In other embodiments, the grasping step further comprises advancing a snare sleeve distally over the snare to collapse the snare.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of a pacemaker retrieval catheter system.

FIGS. 2A-2C show various close-up views of a distal portion of a retrieval catheter system.

FIGS. 3A-3B illustrate a protective sheath of a retrieval catheter system.

FIG. 4 shows a proximal portion of a retrieval catheter system including a handle.

FIGS. 5A-5B illustrate operation of the handle of a retrieval catheter system.

FIGS. 6A-6C show various embodiments of a retrieval catheter system including pre-bent curves in the catheter shaft.

FIGS. 7A-7E illustrate several embodiments of a docking cap of a retrieval catheter system.

FIGS. 8A-8C show a pacemaker being retrieved by a retrieval catheter system when the catheter is not aligned with the pacemaker.

FIGS. 9A-9B are various views of one embodiment of a pacemaker having a retrieval feature.

FIGS. 10A-10B are various views of another embodiment of a pacemaker having a retrieval feature.

DETAILED DESCRIPTION

Various embodiments for delivering system comprising one or more leadless cardiac pacemakers or biostimulators are described. A leadless cardiac pacemaker can communicate by conducted communication, representing a substantial departure from conventional pacing systems. For example, an illustrative cardiac pacing system can perform cardiac pacing that has many of the advantages of conventional cardiac pacemakers while extending performance, functionality, and operating characteristics with one or more of several improvements.

In some embodiments of a cardiac pacing system, cardiac pacing is provided without a pulse generator located in the pectoral region or abdomen, without an electrode-lead separate from the pulse generator, without a communication coil or antenna, and without an additional requirement on battery power for transmitted communication.

An embodiment of a cardiac pacing system configured to attain these characteristics comprises a leadless cardiac pacemaker that is substantially enclosed in a hermetic housing suitable for placement on or attachment to the inside or outside of a cardiac chamber. The pacemaker can have two or more electrodes located within, on, or near the housing, for delivering pacing pulses to muscle of the cardiac chamber and optionally for sensing electrical activity from the muscle, and for bidirectional communication with at least one other device within or outside the body. The housing can contain a primary battery to provide power for pacing, sensing, and communication, for example bidirectional communication. The housing can optionally contain circuits for sensing cardiac activity from the electrodes. The housing contains circuits for receiving information from at least one other device via the electrodes and contains circuits for generating pacing pulses for delivery via the electrodes. The housing can optionally contain circuits for transmitting information to at least one other device via the electrodes and can optionally contain circuits for monitoring device health. The housing contains circuits for controlling these operations in a predetermined manner.

In some embodiments, a cardiac pacemaker can be adapted for delivery and implantation into tissue in the human body. In a particular embodiment, a leadless cardiac pacemaker can be adapted for implantation adjacent to heart tissue on the inside or outside wall of a cardiac chamber, using two or more electrodes located on or within the housing of the pacemaker, for pacing the cardiac chamber upon receiving a triggering signal from at least one other device within the body.

Self-contained or leadless pacemakers or other biostimulators are typically fixed to an intracardial implant site by an actively engaging mechanism or primary fixation mechanism such as a screw or helical member that screws into the myocardium. Examples of such leadless biostimulators are described in the following publications, the disclosures of which are incorporated by reference: (1) U.S. application Ser. No. 11/549,599, filed on Oct. 13, 2006, entitled “Leadless Cardiac Pacemaker System for Usage in Combination with an Implantable Cardioverter-Defibrillator”, and published as US2007/0088394A1 on Apr. 19, 2007; (2) U.S. application Ser. No. 11/549,581 filed on Oct. 13, 2006, entitled “Leadless Cardiac Pacemaker”, and published as US2007/0088396A1 on Apr. 19, 2007; (3) U.S. application Ser. No. 11/549,591, filed on Oct. 13, 2006, entitled “Leadless Cardiac Pacemaker System with Conductive Communication” and published as US2007/0088397A1 on Apr. 19, 2007; (4) U.S. application Ser. No. 11/549,596 filed on Oct. 13, 2006, entitled “Leadless Cardiac Pacemaker Triggered by Conductive Communication” and published as US2007/0088398A1 on Apr. 19, 2007; (5) U.S. application Ser. No. 11/549,603 filed on Oct. 13, 2006, entitled “Rate Responsive Leadless Cardiac Pacemaker” and published as US2007/0088400A1 on Apt. 19, 2007; (6) U.S. application Ser. No. 11/549,605 filed on Oct. 13, 2006, entitled “Programmer for Biostimulator System” and published as US2007/0088405A1 on Apt. 19, 2007; (7) U.S. application Ser. No. 11/549,574, filed on Oct. 13, 2006, entitled “Delivery System for Implantable Biostimulator” and published as US2007/0088418A1 on Apr. 19, 2007; and (8) International Application No. PCT/US2006/040564, filed on Oct. 13, 2006, entitled “Leadless Cardiac Pacemaker and System” and published as WO07047681A2 on Apr. 26, 2007.

In addition to the primary fixation mechanism, such as a helix, some pacemakers may further include a secondary fixation mechanism to provide another feature for keeping the biostimulator in place within the body. Secondary fixation mechanisms can be either active (e.g., the secondary fixation mechanism can actively engage tissue, either within or outside the heart), or can be passive (e.g., the secondary fixation mechanism is not attached to tissue but rather prevents the biostimulator from moving around in the body in the case of accidental detachment). Further details on secondary fixation mechanisms can be found in U.S. application Ser. No. 12/698,969.

Self-contained or leadless pacemakers or other biostimulators are typically fixed to an intracardial implant site by an actively engaging mechanism such as a screw or helical member that screws into the myocardium. In case of malfunction, it is highly desirable to be able to retrieve the leadless pacemaker of biostimulators both acutely (during the implantation procedure) or chronically, after a period of time post implantation minimally invasively.

FIG. 1 illustrates a pacemaker retrieval catheter 100 configured for retrieval of a leadless pacemaker 102 from a patient. More specifically, the catheter 100 is configured to remove a leadless cardiac pacemaker from the heart of a patient. The retrieval catheter 100 can include docking cap 104, catheter shaft 106, protective sheath 107, handle 108, snare slider 110, guide catheter shaft 111, deflection arm 112, and flush ports 114 a, 114 b, and 114 c.

The leadless cardiac pacemaker 102 can be, for example, similar to the pacemakers described above in the referenced applications. The catheter shaft can be made from braided shaft (e.g. pebax with stainless steel braid) and can include segments with different stiffness's throughout the shaft. The deflection knob 112 can be used to steer and guide the catheter during removal of the pacemaker. Snare slider 110 can be configured to control operation of the snare for capturing a leadless cardiac pacemaker, and will be described in more detail below. The flush ports 114 a, 114 b, and 114 c can be used to flush saline or other fluids through the catheter, guide catheter and pacemaker capture sheath.

Sheath 107 can be advanced longitudinally over catheter shaft 106 and guide catheter shaft 111 to cover the pacemaker during retrieval and prevent the pacemaker from catching onto or damaging tissue. In some embodiments, the sleeve can include a radio-opaque coating, such as barium sulfate, or alternatively, can include a platinum or metal feature at the distal end of the sleeve, so that under visualization a user can determine when the sleeve is fully covering the pacemaker prior to removal.

FIG. 2A illustrates a close-up view of one embodiment of a distal portion of the pacemaker retrieval catheter 100 shown in FIG. 1. The distal portion of the retrieval catheter can include snare 203 configured to grasp a leadless cardiac pacemaker or other medical device, and docking cap 204 configured to allow docking of the leadless pacemaker with the retrieval catheter after engaging the pacemaker with the snare. FIG. 2A also illustrates catheter shaft 206 terminating at the docking cap 204, and protective sheath 207 positioned along the shaft slightly proximal to the docking cap and leadless pacemaker.

As shown in FIG. 2A, the snare 203 can comprise at least one loop 216 extending from the catheter shaft. As the snare is advanced distally out of the retrieval system from docking cap 204, the loops can expand in size to aid a user in positioning the snare around or in proximity to the pacemaker to be retrieved. In some embodiments, as in FIG. 2A, the snare can include multiple loops, such as three loops. However, any number of loops can be used as long as the catheter shaft contains sufficient volume to accommodate the loops.

In another embodiment, as shown in FIG. 2B, the snare can include only a single loop. Also shown in FIG. 2B, the loops can include any number of features 218 to aid in grasping a pacemaker or medical device for retrieval. In FIG. 2B, the feature 218 can comprise, for example, a notch feature. In some embodiments, the loops of the snare can be positioned off axis from the center of the catheter shaft to aid in keeping the pacemaker in line with the catheter during removal. For example, in FIG. 2B, the single loop snare 203 can include a notch feature 218 and be positioned off axis from the longitudinal axis of the catheter shaft 206. Since the snare is off axis from the catheter, the snare can be looped around retrieval feature 220 of the pacemaker by positioning the catheter adjacent to the pacemaker and allowing the loop to come into contact with the housing of the pacemaker. As the catheter is pulled away from the pacemaker, the snare can slide up the pacemaker, and notch feature 218 can be allowed to engage the retrieval feature of the pacemaker.

FIG. 2C illustrates the snare 203 grasping a retrieval feature 220 of the leadless cardiac pacemaker 202. In the illustrated embodiment, snare locking sleeve 205 can be advanced distally over the snare from docking cap 204 of the catheter. As the snare locking sleeve advances distally along the snare, it can cause the loops of the snare to reduce in size, thereby grasping or locking onto the retrieval feature 220 of the pacemaker. In some embodiments, the snare locking sleeve 205 can also comprise a torque shaft that runs through the length of the catheter. Details of the torque shaft will be described in more detail below, but generally the torque shaft can be rotated independently of the catheter shaft and coupled to the docking cap of the catheter to apply rotational torque to the docking cap, and thus, to a pacemaker or medical device to be retrieved. In embodiments where the snare includes a plurality of loops, it may be more likely that one of the loops will grasp the pacemaker than in embodiments where the snare comprises only a single loop.

FIG. 3A illustrates a close-up view of the distal portion of the retrieval catheter with the snare locked onto the retrieval feature (not shown) of the leadless pacemaker 302 and docked within docking cap 304. In some embodiments, as will be described in more detail below, the docking cap can include a key or interference feature configured to mate with and engage a corresponding key or feature on the pacemaker itself. In some embodiments, the key or slot on the docking cap can match a unique shape or feature of the retrieval feature of the pacemaker itself. Because the key or slot on or in the docking cap can mate with and engage the key or slot on the pacemaker, the retrieval catheter can be configured to apply torque to the pacemaker to unscrew and remove the pacemaker from tissue. FIG. 3A also illustrates protective sheath positioned slightly proximally to the docking cap 304 along the catheter shaft of the retrieval system.

As shown in FIG. 3A, the docking cap 304 can include ball bearings 309 which allow the docking cap to be free-rotating from the rest of the catheter shaft. This effectively reduces the removal torque and additional forces from the catheter body. The docking cap can be selectively coupled to a torque shaft (not shown) that extends through the length of the catheter to a torque knob on the handle (described below). When the torque shaft is coupled to the docking cap, rotation or actuation of the torque knob rotates the torque shaft, thereby rotating the docking cap 304 at the end of the retrieval catheter. In some embodiments, the docking cap can include a keyed portion or interference feature so as to apply additional torque to the pacemaker when unscrewing.

In FIG. 3B, the protective sheath 307 is shown disposed over the leadless cardiac pacemaker and positioned at the distal end of guide catheter shaft 311. As described above, the protective sheath can be configured to slide over the pacemaker to prevent any sharp edges or features of the pacemaker from tearing, damaging, or catching onto tissue during removal of the pacemaker. The protective sheath can be slidable along a longitudinal axis of the catheter so as to allow for covering and uncovering of the pacemaker with the sheath. In some embodiments, the protective sheath can include other form factors than illustrated in FIG. 3B. For example, in some retrieval scenarios where vegetative growth over the device is significant, the protective sheath may be of a larger diameter to accommodate the increase in size of the device.

The above description of FIGS. 1-3B can be used to illustrate one embodiment of a method of retrieving a medical device or leadless cardiac pacemaker from a patient. First, a retrieval catheter can be advanced into a patient until the docking cap of the catheter is in the vicinity of the pacemaker. Next, the snare of the retrieval catheter can be advanced distally outward from the catheter to surround the retrieval feature of the pacemaker. Once the snare is surrounding the retrieval feature of the pacemaker, the snare locking sleeve/torque shaft can be advanced distally along the snare to close the snare, causing the snare to grasp the retrieval feature of the pacemaker. Next, the snare and snare locking sleeve can be pulled proximally towards the docking cap of the catheter so as to engage the proximal end or retrieval feature of the pacemaker. Rotational torque can then be applied by the catheter to the pacemaker via the torque shaft and docking cap to unscrew the pacemaker from the tissue. The protective sheath can be advanced over the pacemaker, and the pacemaker can then be removed from the patient.

FIG. 4 is a view of the proximal section of the retrieval catheter, showing pacemaker capture sheath 413, handle 408, snare slider 410, deflection arm 412, and flush ports 414 a, 414 b, and 414 c. Deflection and steering of the distal portion of the catheter, including the portion of the catheter with the docking cap (shown above) can be achieved by manipulating the deflection arm 412 of handle 408. Opening and closing the loops of the snare (as illustrated in FIGS. 2A-2C) can be achieved by manipulating the snare slider 410 on the handle in the proximal and distal directions. Although the deflection arm and snare sliders are illustrated as mechanical features, it should be understood that various solutions can be used to steer the catheter and manipulate the snare. For example, the handle can include any number of mechanical features such as rotating knobs or sliding levers, or alternatively, can employ an electronic or hydraulic system with buttons and electric motors or hydraulic pistons. Once the pacemaker is snared and removed from within the heart of the patient (e.g., from within the right ventricle), the pacemaker can be pulled into the capture sheath 413. The capture sheath and pacemaker can then be withdrawn together from an introducer/trocar inserted in the patient (e.g., in the femoral vein). The capture sheath allows the pacemaker to cross a hemostatic seal provided by the introducer without damaging itself or the seal of the introducer.

A portion of the handle can comprise a torque knob 422 which controls rotation of the snare and/or docking cap of the retrieval catheter. The torque knob can be coupled to the docking cap via a torque shaft (not shown) that runs throughout the catheter shaft of the retrieval catheter. The torque knob can also be coupled to the snare, which runs also through the catheter shaft. Rotation of the torque knob clockwise or counter-clockwise can cause rotation of the torque shaft and thus, the docking cap. Longitudinal movement of the torque knob along the handle can slide the snare longitudinally within the catheter.

FIGS. 5A-5B illustrate how manipulation of the various features on the handle control the snare and snare locking sleeve on the distal portion of the catheter. In FIG. 5A, sliding snare slider 510 distally or forward can advance snare locking sleeve 505 over the snare, causing the snare to close around a retrieval feature of the pacemaker 502. As the locking sleeve advances over the snare, the diameter of the snare loop closes which locks the snare loop onto the retrieval feature of the pacemaker. Next, the torque knob 522 can be moved proximally, as shown in FIG. 5B, pulling the snare and snare locking sleeve proximally and causing the pacemaker 502 to come into contact with and dock within docking cap 504. In some embodiments, pulling the snare locking sleeve proximately can cause the snare to engage and become coupled with the docking cap. When the snare locking sleeve (also referred to as a torque shaft) is coupled to the docking cap, rotation of the torque sleeve causes the docking cap to rotate as well.

FIG. 6A illustrates one embodiment of a pacemaker retrieval catheter 600 having a pre-curved catheter shaft. The catheter may include a distal curve 624 to enhance steering and navigation of the retrieval catheter. In some embodiments, the distal curve can improve steering and navigation of the retrieval catheter by providing mechanical support that the tissue and vein structures may lack. In one embodiment of the retrieval system, the distal section of the guide catheter may be pre-curved to a 90 degree angle and 30 mm radius. The catheter may include a flush port on the proximal end to allow aspiration or irrigation of the guide catheter lumen. FIG. 6B is a close-up view of the distal section of the retrieval catheter with the snare retracted and showing the distal curve 624 of the catheter shaft. In some embodiments, the shaft can include a curve angle from 0-180 degrees and curve radius of 20-50 mm. FIG. 6B shows the retrieval catheter in the vicinity of the pacemaker 602, with the snare retracted into the catheter.

FIG. 6C is another close-up view of the distal section of a retrieval catheter with the snare retracted showing a distal curve 606 of approximately 180 degrees. In this embodiment, the 180 degree distal curve enables the retrieval catheter to be able to access pacemakers whose proximal caps are rotated 180 degrees from the point of entry of the catheter.

FIGS. 7A-7C show various views of one embodiment of a docking cap 704. The docking cap of FIGS. 7A-7C can be used in the systems described above. In FIG. 7A, a distal tip of the docking cap can include scallop features 726. As shown in FIG. 7A, the scallop features can comprise a series of curves or cutouts into the distal end of the docking cap. FIG. 7A illustrates four scallop features, however in other embodiments different numbers of scallop features can be used, such as one, two, three, or more than four scallop features. The scallop features are configured to prevent the docking cap from binding in a perpendicular configuration with a leadless pacemaker during retrieval, as will be described below. The scallop features can include not only curved cutouts, as shown, but can also be sloped or beveled inwards towards the interior of the docking cap. This feature can aid the docking cap in assuming an aligned, co-linear configuration with the medical device to be retrieved.

FIG. 7B is a cutaway view of the docking cap of FIG. 7A, and illustrates a keyed portion or interference feature 728 disposed on the inside of the docking cap 704. The keyed portion can be configured to align with or engage a matching keyed portion or feature on the medical device to be retrieved. For example, using the leadless cardiac pacemaker described above as an example, the retrieval feature of the pacemaker can include a corresponding keyed portion or feature designed to engage the keyed portion 728 of the docking cap. When the docking cap is rotated, the keyed portions can engage one another to provide additional torque to the pacemaker, such as when unscrewing the pacemaker from tissue.

FIG. 7C illustrates a perspective view of a docking cap including an interference feature 728 disposed inside the docking cap 704. FIG. 7C illustrates a retrieval feature 720 of a medical device, such as a leadless cardiac pacemaker, disposed within the docking cap and coming into contact with the interference feature 728 of the docking cap. As shown in FIG. 7C, the retrieval feature can be disposed within the docking cap at an angle, yet still engaging the interference feature of the pacemaker. As will be described in more detail below, when the retrieval feature 720 is attached to the pacemaker with a flexible stem or flexible attachment, it allows the retrieval feature to bend as it is pulled within the docking cap. This allows the docking cap to still apply rotational torque to the retrieval feature and the pacemaker via interference feature 728 even when the pacemaker is not aligned longitudinally with the retrieval catheter and docking cap.

FIG. 7D illustrates a top down view of the docking cap 704, looking into the docking portion from the distal end. As shown, the docking cap can include a recessed slot 730 sized and shaped to receive a key feature of the torque shaft (or snare locking sleeve) of the retrieval catheter. In FIG. 7C, the recessed slot 730 is illustrated as being square in shape. This recessed slot is therefore sized and configured to receive a key on the torque shaft having a square shape. It should be understood that any size or shape recessed slot can be used, and that a corresponding key feature on the torque shaft should be similarly sized and shaped to mate with the slot.

When the key feature of the torque shaft is aligned with the recessed slot 730 of the docking cap, the torque shaft is effectively coupled to the docking cap of the catheter. This coupling allows the torque shaft to apply rotational torque to the docking cap. If the torque shaft is advanced distally through the slot 730 so that the slot does not align with the key feature of the torque shaft, then the torque shaft is not coupled to the docking cap, and the two are free to rotate relative to another. Thus, when the torque shaft (also referred to herein as the snare slider) is advanced distally to close the snare, the torque shaft can become decoupled from the docking cap. When the torque shaft and snare are then pulled proximately into the docking cap, the key feature of the torque shaft can align with the slot 730 of the docking cap, allowing the torque shaft to apply torque to the docking cap to unscrew the pacemaker from tissue. The key feature of the torque shaft is also shown in FIG. 7E.

FIG. 7D also illustrates a lumen 731 disposed in the docking cap. The lumen can be, for example, a hollow portion of the torque shaft. The lumen of the torque shaft can house the snare, described above, allowing the snare to be advanced distally from the docking cap. Also as described above, when the snare is advanced distally from the docking cap, advancing the torque shaft distally over the snare can cause the loop(s) of the snare to close around a pacemaker to be retrieved.

FIG. 7E illustrates another cutaway view of the docking cap. In FIG. 7E, the torque shaft or snare locking sleeve 705 has been advanced slightly within the docking cap, illustrating key feature 733 of the torque shaft being decoupled from slot 730 of the docking cap. When the key torque shaft is decoupled from the docking cap, as described above, rotation of the torque shaft does not cause the docking cap to rotate. However, if the key feature 733 of FIG. 7E was pulled back proximally to engage slot 730 of the docking cap, then the torque shaft and docking cap would be coupled together, and rotation of the torque shaft would apply rotational torque to the docking cap.

FIGS. 8A-8B illustrate various embodiments of a docking cap 804 having scallop features 826 engaging a medical device or pacemaker 802. As described above in FIG. 7A, scallop features 826 on a distal portion of the docking cap can prevent the docking cap from binding perpendicularly with a medical device during retrieval. In FIG. 8A, the retrieval catheter and docking cap 804 are shown approaching the pacemaker 802 in a substantially perpendicular configuration. The catheter is shown without the snare (as described above) for simplicity. Referring to FIG. 8B, once the snare (not shown) has grasped the retrieval feature 820 of pacemaker 802, the catheter, and docking cap 804, can swing upwards, as indicated by arrows AA, due to the scallop features 826 of the docking cap. FIG. 8C illustrates the docking cap 804 and retrieval catheter in the co-linear configuration with retrieval feature 820 of pacemaker 802, as a result of scallop features 826.

FIGS. 9A-9B and 10A-10B show multiple views of various embodiments of retrieval features on a leadless cardiac pacemaker. The retrieval features illustrated in these figures can be grasped by the snare of the retrieval catheters described herein, and can also be configured to dock within the docking cap of the retrieval catheter.

In FIGS. 9A-9B, the retrieval feature comprises a “button” or circular grasping feature 932. The grasping feature 932 can be attached to the pacemaker 902 via at least one flexible stem 934. The flexible stem allows for easier capturing of the pacemaker into the docking cap by allowing the grasping feature and stem(s) to “bend” into the docking cap when the retrieval catheter is off-axis from the pacemaker during a retrieval attempt. The flexible stem(s) also allow the grasping feature 932 to orient itself within the snare and to compensate for the asymmetry of the snare to allow it to align the docking cap with the pacemaker. Additionally, the flexible stem deflection permits torque transmission from the catheter to the leadless pacemaker. The flexible stem can be made of materials such as nitinol, stainless steel or titanium cable, MP35N, or other similar materials. The flexible stem may be connected to the grasping feature and the proximal end of the leadless pacemaker by laser welding, soldering, or other manufacturing processes know in the art.

Also shown in FIG. 9A, a proximal portion of the pacemaker 902 can include a key feature 936. The key feature 936 can be sized and configured to mate with the interference feature within the docking cap, as described above. The key feature of the pacemaker and the interference feature of the docking cap and catheter can allow the torque shaft and docking cap of the catheter to apply rotational torque to the pacemaker, such as to unscrew the pacemaker from tissue during retrieval.

FIGS. 10A-10B illustrate another embodiment of a “hook shaped” retrieval feature 1032 on the pacemaker 1002. The hook shaped proximal cap can allow for easier grasping by the snare. The “hook shaped” retrieval feature can provide an easily accessible yet atraumatic surface for the snare to grasp. In some embodiments, a base portion 1034 of the hook shaped feature can comprise a flexible material, as described above with respect to the flexible stems of the “button” shaped retrieval feature in FIGS. 9A-9B. The hook shaped retrieval feature can also include cutouts 1038 that can serve a similar purpose to the key feature described above in FIGS. 9A-9B. The cutouts can engage, for example, similarly shaped features in the docking cap or retrieval catheter to allow the catheter to apply rotational torque to the pacemaker for unscrewing the pacemaker from tissue.

As described above, the docking cap itself can include cutouts or recessed slots configured to mate with or engage the retrieval feature of the pacemaker. For example, the circular retrieval feature of FIGS. 9A-9B can mate with a similarly shaped recessed slot within the docking cap. Similarly, the hook shaped retrieval feature of FIGS. 10A-10B can mate with a similarly shaped recessed slot within the docking cap.

As for additional details pertinent to the present invention, materials and manufacturing techniques may be employed as within the level of those with skill in the relevant art. The same may hold true with respect to method-based aspects of the invention in terms of additional acts commonly or logically employed. Also, it is contemplated that any optional feature of the inventive variations described may be set forth and claimed independently, or in combination with any one or more of the features described herein. Likewise, reference to a singular item, includes the possibility that there are plural of the same items present. More specifically, as used herein and in the appended claims, the singular forms “a,” “and,” “said,” and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation. Unless defined otherwise herein, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The breadth of the present invention is not to be limited by the subject specification, but rather only by the plain meaning of the claim terms employed. 

What is claimed is:
 1. A leadless pacemaker, comprising: a housing having a central axis; a plurality of electrodes coupled to the housing; a fixation mechanism at a distal end of the housing; and a retrieval feature at a proximal end of the housing, wherein the retrieval feature includes a grasping feature connected to the housing by a stem, wherein a plurality of cutouts extend into the grasping feature to a transverse member, wherein the transverse member extends transverse to the central axis to define a gap on the central axis between the transverse member and the housing, and wherein the gap is configured to receive a snare.
 2. The leadless pacemaker of claim 1, wherein the central axis extends through the transverse member.
 3. The leadless pacemaker of claim 2, wherein the stem is transversely offset from the central axis.
 4. The leadless pacemaker of claim 1, wherein the cutouts are on opposite sides of the transverse member.
 5. The leadless pacemaker of claim 4, wherein the cutouts allow a docking cap of a delivery system to apply rotational torque to the leadless pacemaker.
 6. The leadless pacemaker of claim 1, wherein the retrieval feature extends proximally from a distal end of the stem at the proximal end of the housing to a proximal atraumatic surface of the grasping feature.
 7. The leadless pacemaker of claim 1, wherein the stem is flexible.
 8. A leadless pacemaker system, comprising: a leadless pacemaker including a housing having a central axis, a plurality of electrodes coupled to the housing, a fixation mechanism at a distal end of the housing, and a retrieval feature at a proximal end of the housing, wherein the retrieval feature includes a grasping feature connected to the housing by a stem, wherein a plurality of cutouts extend into the grasping feature to a transverse member, wherein the transverse member extends transverse to the central axis to define a gap on the central axis between the transverse member and the housing, and wherein the gap is configured to receive a snare; and a delivery system including a docking cap to receive the retrieval feature of the leadless pacemaker.
 9. The leadless pacemaker system of claim 8, wherein the central axis extends through the transverse member.
 10. The leadless pacemaker system of claim 9, wherein the stem is transversely offset from the central axis.
 11. The leadless pacemaker system of claim 8, wherein the cutouts are on opposite sides of the transverse member.
 12. The leadless pacemaker system of claim 11, wherein the cutouts allow the docking cap of the delivery system to apply rotational torque to the leadless pacemaker.
 13. The leadless pacemaker system of claim 8, wherein the retrieval feature extends proximally from a distal end of the stem at the proximal end of the housing to a proximal atraumatic surface of the grasping feature.
 14. A method, comprising: grasping, by a snare, a retrieval feature of a leadless pacemaker, wherein the leadless pacemaker includes a housing having a central axis, a plurality of electrodes coupled to the housing, a fixation mechanism at a distal end of the housing, and the retrieval feature at a proximal end of the housing, wherein the retrieval feature includes a grasping feature connected to the housing by a stem, wherein a plurality of cutouts extend into the grasping feature to a transverse member, wherein the transverse member extends transverse to the central axis to define a gap on the central axis between the transverse member and the housing, and wherein the gap is configured to receive a snare; and advancing a snare locking sleeve over the snare to close the snare around the retrieval feature.
 15. The method of claim 14, wherein the central axis extends through the transverse member.
 16. The method of claim 15, wherein the stem is transversely offset from the central axis.
 17. The method of claim 14 further comprising engaging, by a docking cap of a delivery system, the cutouts on opposite sides of the transverse member.
 18. The method of claim 17 further comprising rotating the delivery system to apply rotational torque to the leadless pacemaker.
 19. The method of claim 14, wherein the retrieval feature extends proximally from a distal end of the stem at the proximal end of the housing to a proximal atraumatic surface of the grasping feature. 